"We began rolling out shared itineraries in January in a handful of markets, and we've gradually ramped up the initiative where we now connect our entire network across both Southwest and AirTran," Bob Jordan, Southwest's chief commercial and president of AirTran, says in a release. "With a connected network, we can offer Customers more itineraries, more destinations, more low fares, and a taste of what's to come once the integration is complete."
The linking of the networks opens the route maps of both carriers to passengers of either airline. For example, citys such as Richmond and Memphis still have service only on AirTran. So, before the linking of the carriers' schedules, customers from those cities could only connect to Southwest flights by buying two separate itineraries.
(Read more: Southwest Airlines Adds $40 Fee for Early Boarding)
Now, however, they can buy a single-ticket itinerary that includes and AirTran flight to Atlanta and a connecting Southwest flight to a destination elsewhere.
The linking of the networks also means Southwest customers can now buy tickets on AirTran's international routes, which include Aruba, the Bahamas, Bermuda, the Dominican Republic, Jamaica and Mexico. (Read more: More Destinations as Southwest, AirTran Blend Frequent Flier Perks)
Those destinations are currently served only by AirTran as Southwest makes upgrades to its booking system that eventually will allow it to sell international itineraries.
Southwest plans to assimilate all of AirTran's operations into its own and discontinue the AirTran brand, though that will take another year or more to complete.
Southwest calls its "transition to a single ticketing system" "a large and complex process that is expected to be completed by the end of 2014." Some industry observers, however, have speculated that could slide into 2015.